Sound-reproducing device



Dec. 13, 1960 R. T. CHRISTENSEN SOUND-REPRODUCING DEVICE Filed Aug. 1, 1956 RAYMON D I. CHRISTENSEN B INVENTOR.

BY AMPLIFIER HIS ATTORNEY.

2,964,596 SOUND-REPRODUCING DEVICE Raymond T. Christensen, Itasca, Ill., assignor to Zenith Radio Corporation, a corporation of Delaware Filed Aug. 1, 1956, Ser. No. 601,569-

4 Claims. (Cl. 17-107) This invention relates to sound-reproducing devices of the hearing aid type suitable for use with an ear mold.

When a custom-fitted hearing aid ear mold is inserted in the auditory canal and a sound-reproducing device or earphone is connected to or plugged into the mold, an acoustically sealed air chamber is established, being formed by the vibratory diaphragm in the earphone, the sound-communicating passageway through the ear mold and the ear drum of the wearers ear. Such acoustic sealing is desirable for eflicient operation of the hearing aid, but it does present a disadvantage. When the atmospheric pressure changes, which occurs, for example, in ascending or descending in an elevator, the air in the sealed chamber remains at the previous pressure resulting in a differential with the atmosphere. Consequently, an annoying pressure builds up on one surface of the ear drum, the outside area when the atmospheric pressure decreases and the internal surface when the atmosphere pressure increases.

This problem has been overcome in previous hearing aid assemblies by including a venting channel in the ear mold which extends from the exposed surface to the passageway. Such a vent does equalize the pressure, but unless it is properly positioned, the frequency response characteristic of the hearing aid is altered to the extent that many frequency components normally reproduced are lost. It is a difficult and delicate operation to drill or bore a hole through an ear mold primarily because every custom-made mold is shaped differently. The shape variations require that each ear mold be drilled from a slightly different angle. Consequently, the in-' ability to utilize the mass production techniques makes the drilling operation relatively expensive.

The present invention provides for venting of the sealed air chamber in an inexpensive manner conducive to the use of mass production techniques. Instead of drilling a hole through the ear mold itself, a channel is bored through the case of the earphone or sound-reproducing device from a point on the external surface which is exposed to the atmosphere, to the air chamber. In order not to deleteriously affect the frequency response charatceristic of the hearing aid apparatus, the venting channel must exhibit a predetermined combination of length and cross-sectional area. If a hole is drilled in a direction perpendicular to the surface of a case having conventional thickness, the vent will be too short for a practicable area and the frequency response characteristic will be deteriorated. One of the salient features of the present invention resides in the provision of a venting channel of sufficient length (greater than the thickness of the case) in order to have no affect on the frequency response. 7

It is an object, therefore, to provide a new and improved sound-reproducing device for use in hearing aid apparatus.

It is another object of the present invention to provide a sound-reproducing device for use with a hearing aid ear mold which prevents substantial static pressure differences from existing between the sound-communicating passageway within the. ear mold and the outer atmosphere.

It is still another object of the invention to provide such an improved sound-reproducing device which does not deleteriously affect the frequency response characteristic.

nited States Patent "ice It is a further object of the invention to provide a sound-reprodncing device which includes a vent to relieve pressure differentials between the air chamber and the outer atmosphere, which vent may be provided by utilization of mass production techniques.

A miniature sound-reproducing device for use in conjunction with a hearing aid amplifier unit and an ear mold adapted for acoustically sealed insertion in the auditory canal, constructed in accordance with the invention, comprises means including an electromechanical transducer having a vibratory diaphragm and coupled to the amplifier unit for vibrating the diaphragm to reproduce sound impressed on the amplifier unit. Means including a case enclosing the transducer is adapted for attachment to the ear mold for providing a sound-communicating passageway from the diaphragm through the ear mold.

partially determined by the acoustic characteristics of the sound-communicating passageway. Finally, the case is vented to prevent substantial static pressure difierentials between the sound-communicating passageway and the outer atmosphere without deleteriously alfecting the frequency response characteristic.

The features of this invention which are believed to be new are set forth with particularity in the appended claims. The invention, together wtih further objects and advantages thereof, may best be understood, however, by reference to the following description in conjunction with the accompanying drawing, the single figure of which is a side view of a sound-reproducing device constructed in accordance with the invention, and the manner in which it is associated with a human ear, certain portions of the drawing being in section for illustrative purposes.

A hearing aid sound-reproducing device 10 includes the usual windings 11, pole piece 12, and vibratory diaphragm 14, which together respond to signals translated to windings 11 via conductors 15 from a hearing aid amplifier unit 13. The electromechanical transducer elements 11, 12 and 14 are housed in an enclosure comprising a rear cover 17, constructed preferably of plastic, and a front cover or case 18. Case 18, which is preferably made of some suitable metal and is circular in outline looking in a direction perpendicular to the plane of diaphragm 14 (not shown in the drawing), has a thickness characteristic varying in concentric steps toward its center to provide a plurality of setbacks 16 on its internal surface, namely the surface of case 18 adjacent diaphragm 14. A minor portion of the external surface of case 18 is curved while the major portion is substantially flat. Case 18 also has a projection 20 which is shaped to mate with a recess in an ear mold 22. A resilient ring 23 which encircles the recess in and is attached to mold 22 retains projection 20 in place once it is plugged into the recess. Mold 22 also has a substantially flat portion which is parallel with the flat portion phragm 14 forming one end and the ear drum (not shown) of ear 25 forming the other. Sound-reproducing device 10 exihibits a frequency response characteristic over a given range, namely the portion of the spectrum containing the various frequency components normally translated through hearing aid apparatus, which is at least Patented Dec. 13, 1950 The sound-reproducing device exhibits a fre-' quency response characteristic over a given range at least partially determined by the acoustic characteristics of sound-communicating passageway 26.

Thus far, the various elements described represent well known construction for a sound-reproducing device and its association with hearing aid apparatus. However, in order to provide static pressure equivalence between sound-communicating pasageway 26 and the outer atmosphere in accordance with the invention, a vent 28 is bored from a point on the curved external surface of case 18 to one of the setback points 16 on the internal surface of case 18, at an acute angle with respect to the flat portion of the external surface of case 18. By placing venting channel 28 in that manner, a bore of practicable area with a length sufficient to have no adverse effect on the frequency response characteristic is obtained; the length of vent 28 is considerably greater than the maximum thickness of case 18.

It will be appreciated that because of the standardization of sound reproducer 10, namely since it can be used with any ear mold 22 either of so-called standard construction or custom fitted to the wearer, vent 28 may be drilled or bored into case 18 by means of Well known production techniques. In addition to effecting a considerable cost saving the construction of the invention provides complete standardization of tone or frequency response of the earphone-ear mold assembly, regardless of any variations in size and shape between individually fitted ear molds. Moreover, it has been found that the illustrated construction tends to render a more mellow and pleasing reproduction of sound than previously employed reproducers without vent 28, even when the latter are employed with a vented ear mold.

The invention provides, therefore, an improved sound reproducing device of the hearing aid type which prevents a static pressure difference between the outside atmosphere and the air chamber defined by the diaphragm of the sound reproducer, the sound-communicating passageway of the ear mold and the wearers ear drum.

While a particular embodiment of the invention has been shown and described, modifications may be made, and his intended in the appended claims to cover all such modifications as may fall within the true spirit and scope of the invention.

I claim:

1. A miniature sound-reproducing device for use in conjunction with a hearing aid amplifier unit and an ear mold adapted for acoustically sealed insertion in the auditory canal, said device comprising: means including an electromechanical transducer having a vibratory diaphragm and coupled to said amplifier unit for vibrating said diaphragm to reproduce sound impressed on said amplifier unit; and means including a case having a varying thickness enclosing said transducer and adapted for attachment to said ear mold for providing a soundcommunicating passageway from said diaphragm through said ear mold, said sound-reproducing device having a frequency response characteristic which over a given range is at least partially determined by the acoustic characteristics of said sound-communicating passageway, and said case having a venting channel, of a length greater than the maximum thickness of said case, which prevents substantial static pressure differentials between said soundcommunicating passageway and the outer atmosphere without deleteriously affecting said frequency response characteristic.

2. A miniature sound-reproducing device for use in conjunction with a hearing aid amplifier unit and an ear mold adapted for acoustically sealed insertion in the auditory canal, said device comprising: means including an electromechanical transducer having a vibratory diaphragm and coupled to said amplifier unit for vibrating said diaphragm to reproduce sound impressed on said amplifier unit; and means including a case enclosing said transducer and adapted forattachment to said ear mold for providing a sound-communicating passageway from said diaphragm through said ear mold, said sound-reproducing device having a frequency response characteristic which over a given range is at least partially determined by the acoustic characteristics of said sound-communicating passageway, and said case having a venting channel of a length greater than the thickness of said case, which prevents substantial static pressure differentials between said sound-communicating passageway and the outer atmosphere without deleteriously affecting said frequency response characteristic.

3. A miniature sound-reproducing device for use in conjunction with a hearing aid amplifier unit and an ear mold adapted for acoustically sealed insertion in the auditory canal, said device comprising: means including an electromechanical transducer having a vibratory diaphragm and coupled to said amplifier unit for vibrating said diaphragm to reproduce sound impressed on said amplifier unit; and means including a case enclosing said transducer and adapted for attachment to said ear mold for providing a sound-communicating passageway from said diaphragm through said ear mold, said soundreproducing device having a frequency response characteristic which over a given range is at least partially determined by the acoustic characteristics of said soundcommunicating passageway, and said case having a venting channel, extending from a point on its external surface between said diaphragm and said ear mold to said sound-communicating passageway in a direction substantially parallel to the external surface of said case, which prevents substantial static pressure differentials between said sound-communicating passageway and the outer atmosphere without deleteriously affecting said frequency response characteristic.

4. A miniature sound-reproducing device for use in conjunction with a hearing aid amplifier unit and an ear mold adapted for acoustically sealed insertion in the auditory canal, said device comprising: means including an electromechanical transducer having a vibratory diaphragm and coupled to said amplifier unit for vibrating said diaphragm to reproduce sound impressed on said amplifier unit; and means including a circular case enclosing said transducer and adapted for attachment to said ear mold, said case having a thickness varying in concentric steps towards its center to provide a plurality of setbacks on its internal surface and having a curved 7 external surface between said diaphragm and said ear mold and a substantially flat external surface for engaging the external surface of Said ear mold; said soundreproducing device having a frequency response characteristic which over a given range is at least partially determined by the acoustic characteristics of said soundcommunicating passageway, and said case having a venting channel, of a length greater than the maximum thickness of said case extending therethrough from a point on its curved external surface to one of the setback points on its internal surface and at an acute angle with respect to the flat external surface of said case, which prevents substantial static pressure differentials between said sound-communicating passageway and the outer atmosphere without deleteriously affecting said frequency response characteristic.

References Cited in the file of this patent UNITED STATES PATENTS 1,601,063 Frederick Sept. 28, 1926 2,164,121 Pescador June 27. 1939 2,325,590 Carlisle Aug. 3, 1943 2,363,175 Grossman i Nov. 21, 1944 2,390,794 Knight Dec. 11, 1945 2,820,107 Knauert Ian. 14, 1958 2,874,231 Wallace Feb. 17, 1959 FOREIGN PATENTS 922.889 Germany Jan. 27, 1955 

